Body-centered-cubic CoxFe1-x alloy films have now been grown throughout the range 0 < x < 1 on Ag films. This achievement has made possible the growth of five Fe/Ag/CoxFe1-x sandwiches which are similar except for the Co content of the alloy layer. The anisotropic magnetoresistance of these samples varies linearly with Co fraction, but the giant magnetoresistance shows a non-monotonic behavior. The M-H loops of these samples must be understood in detail in order to intercompare the giant magnetoresistance data because of the need to correct for different magnetic configurations at the MR peak in different samples. Simple sandwich structures are well-suited to fundamental study of GMR in systems without interlayer coupling because the determination of the magnetic configuration of a uncoupled multilayer at the MR peak may be quite difficult. In further studies with variable alloy composition, it would be desirable to use magneto-optic characterization to clarify the magnetization curves of samples with complex behavior.[26] A magneto-optic study of the samples discussed here is already underway.
Why the giant magnetoresistance is larger for some ferromagnet/paramagnet combinations than others remains is as yet an unanswered question. As theorists begin to study this issue using band structure diagrams and density-of-states curves, detailed information on the magnetoresistance of multilayers with alloy magnetic layers will become increasingly useful.
Acknowledgements
The authors would like to thank P. Lubitz for helpful discussions and D. King for technical assistance. At NRL this work was supported by DARPA and ONR. Part of this work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W- 7405-ENG-48.